The present invention relates to a method for treating autism in patients. More particularly, the present invention relates to a method for modulating in vivo levels of glutamine, glycine or both glutamine or glycine in the treatment of autism.
Autism is a developmental disorder characterized by social relating and communicating impairments along with restricted, repetitive or stereotypical behavior and onset by three years of age. A genetic basis for the disorder is suggested by observations such as developmental anomalies in autistic patients, increased incidence of autism in siblings of autistic patients, and a tendency for both of a set of monozygotic twins to be either autistic or not autistic (also called xe2x80x9cconcordancexe2x80x9d for a disorder). However, in 75-80% of autistic individuals, no underlying cause is found for the autism. Previous studies have implicated abnormalities involving neurotransmitters including serotonin, norepinephrine, and histamine in some cases of autism.
U.S. Pat. No. 4,994,467 issued Feb. 19, 1991 to Zimmerman discloses a method for treating autism in children by administration of therapeutically effective amounts of a N-methyl-D-aspartate (NMDA) receptor antagonist selected from the group consisting of ketamine and dextromethorphan.
U.S. Pat. No. 5,008,251 issued Apr. 16, 1991 to Gruber (assigneexe2x80x94Regents of the University of California) discloses methods for treatment of autism comprising administration of the compounds including the purine nucleoside 5-amino-4-imidazolecarboxamide riboside (AlCA riboside), AlCA ribotide, ribavirin, and ribavirin monophosphate.
U.S. Pat. No. 5,866,585 issued Feb. 2, 1999 to Fogel (assigneexe2x80x94Synchroneuron) discloses a method for treating tardive dyskinesia using the NMDA receptor antagonists dextromethorphan and memantine.
U.S. Pat. No. 5,506,231 issued Apr. 9, 1996 to Lipton (assigneexe2x80x94The Children""s Medical Center Corporation) discloses the treatment of damage to the central nervous system in a patient resulting from infection with HIV with an NMDA receptor antagonist, such as dextromethorphan.
U.S. Pat. No. 5,605,911 issued Feb. 25, 1997 to Olney et al., (assigneexe2x80x94Washington University) discloses methods of treating or preventing central nervous system effects resulting from NMDA receptor hypofunction, including schizophrenia. The methods comprise administration to a patient in need thereof of an NMDA antagonist along with an alpha-2 adrenergic receptor agonist; or alternatively, the administration of an alpha-2 adrenergic receptor agonist drug alone.
U.S. Pat. No. 5,576,323 issued Nov. 19, 1996 to Heinz et al. (assigneexe2x80x94Eli Lilly and Company) discloses compounds that affect excitatory amino acid receptors, including the NMDA receptor, and that may be useful in the treatment of neurological disorders.
Despite the disclosure of the foregoing U.S. patents, there remains significant room for improvement in the treatment of autism, particularly in children. A treatment approach that is based on observed biochemical abnormalities in autistic patients would be desirable in view of the potential applicability of such an approach to the 75 to 80% of autistic individuals having primary autism in which no underlying cause is found. Such an approach is not currently available in the art.
A method of treating autism in a patient is disclosed. The method comprises administering to the patient an effective amount of a glutamine level reducing agent, a glycine level reducing agent or combinations of these with or without a modulator of the Gly NMDA receptor.
Accordingly, it is an object of this invention to provide an improved method of treating autism, particularly in children.
It is another object of this invention to provide a method of treating autism that is based on observed biochemical abnormalities in autistic patients.
It is a further object of this invention to provide a method of treating autism that is based on observed elevated levels of glutamine and glycine in autistic patients.
It is still a further object of this invention to provide a method of treating autism that pertains to the modulation of glutamine and glycine levels in autistic patients.
Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds, when taken in connection with the accompanying Examples as best described hereinbelow.
Autism is characterized by deficits in sociability, reciprocal verbal and nonverbal communication, repetitive or stereotypical behavior, and onset by 3 years of age. Most (i.e. about 75-80%) autistic individuals have primary autism in which no underlying cause is found.
In screening a series of consecutive autistic probands, the present co-inventors detected 5/36 (14%) who had elevated plasma levels of glutamine (Gln) or glycine (Gly), or elevated levels of both Gln and Gly, on repeated studies. One patient in the screening series was diagnosed as having autism at age 2 years, 10 months. His Gln (mean 884 xcexcmol/Lxe2x80x94normal 370-682 xcexcmol/L) and Gly (mean 379 xcexcmol/Lxe2x80x94normal 120-315 xcexcmol/L) levels were consistently elevated above the normal range on all 5 studies done between age 4 years, 1 1 months and age 6. Urine Gln and Gly levels were 1410 xcexcmol/g creatinine (normal 165-510 xcexcmol/g creatinine) and 5663 xcexcmol/g creatinine (normal 569-1395 xcexcmol/g creatinine), respectively. His cerebrospinal fluid (CSF) Gln was 708 xcexcmol/L (normal 356-680 xcexcmol/L) while his CSF Gly level was normal. His electrolytes, anion gap and plasma ammonia levels were all well within the normal range and his urine organic acid profile was normal. Another patient in the series had persistent elevated Gly levels on multiple plasma amino acid profiles. These levels ranged from 324-439 xcexcmol/L (normal for age ranges from 120-315 xcexcmol/L).
The present invention thus pertains to the identification of elevated levels of glutamine and glycine as compared to normal levels in autistic patients, and particularly in autistic children. The present invention thus also pertains to a method of treating autism in a patient comprising administering to the patient an effective amount of a glutamine level reducing agent (e.g. phenylbutyrate or PB), a glycine level reducing agent (e.g. sodium benzoate or SB) or combinations of these agents, with or without a modulator of the Gly NMDA receptor (e.g. dextromethorphan or DM). Until the disclosure of the present invention, a role for modulation of in vivo glutamine and glycine levels in the treatment of autism has not been characterized in the art. Correspondingly, prior to the disclosure of the present invention, no motivation can be found in the art to modulate in vivo glutamine and glycine levels in the treatment of autism.
A. General Considerations
Glutamic acid is one of the 20 common amino acids used by all living cells to make protein. The ionized form of glutamic acid, glutamate, is the predominant form of this compound in neutral solutions. In mammals, glutamate serves as the predominant excitatory neurotransmitter in mammalian central nervous systems. See e.g., Olney. J. W., xe2x80x9cGlutamate,xe2x80x9d pp. 468-70 in Encyclopedia of Neuroscience, G. Adelman, ed. (Birkhauser, Boston, 1987). Glutamate (Glu) is also employed in vivo as a precursor in the production of glutamine (Gln), also one of the 20 common amino acids used by all living cells to make protein. As is well known in the art, glutamate and glutamine are structurally very similar, varying only in the presence of an amino group (Gln) instead of a carboxyl group (Glu) on the side chain of each amino acid.
Glutamate exerts its effects on glutamate receptors found on neurons. When the glutamate receptor is activated by glutamate, it changes conformation and alters ion channels that consequently change the chemical ionic gradient across the neuron cell membrane. This mechanism is a basis for nerve signals. Since glutamate is an amino acid that serves as an excitatory neurotransmitter inside the brain, it is often called an xe2x80x9cexcitatory amino acidxe2x80x9d (EM). Glutamate receptors may also be activated by another amino acid, aspartate, and hence glutamate receptors are also called xe2x80x9cEAA receptorsxe2x80x9d. However, glutamate is utilized much more than aspartate as a neurotransmitter, and EAA receptors are more typically referred to as xe2x80x9cglutamate receptorsxe2x80x9d. The N-methyl-D-aspartate (NMDA) receptor is an example of an EAA receptor.
Phenylbutyrate (PB) conjugates to glutamine in vivo and has been used in the art to treat urea cycle disorders. It has thus been reported that phenylbutyrate treatment can decrease plasma glutamine levels. See Darmaun et al., Am. J. Physiol. 274: E801-07 (1998). It has also been reported that phenylbutyrate is rapidly converted in vivo to phenylacetate by first pass liver metabolism. See Piscitelli et al., J. Clin. Pharmacol. 35:368-73 (1995). It has further been reported that phenylacetylglutamine, the amino acid acetylation product of phenylacetate, serves as a waste nitrogen product, and the formation of phenylacetylglutamine reduces glutamine levels. See Brusilow, Pediatr. Res. 29: 147-50 (1991). While it is not the desire of the present co-inventors to be bound by an particular method of action, the lowering of glutamine is contemplated to decrease the stimulation of the EAA receptors that is contemplated to occur in autistic patients with high levels of glutamine.
Glycine has a regulatory binding site on NMDA-type EAA receptors on neurons. Glutamate is the primary neurotransmitter, while glycine plays a co-agonist role. Sodium benzoate is a well known and widely used preservative for pharmaceutical products such as syrups, flavored vehicles, and multiple dose containers for liquid preparations. Sodium benzoate is also used as a diagnostic acid for liver function and as a glycine level reducing agent. Sodium benzoate is thus contemplated to be useful in the treatment of the autistic patients with elevated glutamine or glycine, or both, when administered alone or in conjunction with a glutamine level reducing agent (e.g. phenylbutyrate and phenylacetate) in accordance with the present invention.
Dextromethorphan has as one of its properties the ability to retard glycine binding to an NMDA-type EAA receptor. Hence, dextromethorphan is contemplated to be useful in the treatment of the autistic patients with elevated glutamine or glycine, or both, when administered in conjunction with a glutamine level reducing agent (e.g. phenylbutyrate and phenylacetate) and/or a glycine level reducing agent (e.g. sodium benzoate) in accordance with the present invention.
B. Definitions
The terms xe2x80x9celevated glutamine levelxe2x80x9d or xe2x80x9celevated glycine levelxe2x80x9d are meant to refer to in vivo glutamine or glycine levels that are elevated to any extent over normal ranges of in vivo glutamine levels. Representative normal ranges of glutamine and glycine are disclosed herein. Glutamine and glycine levels are measured in any suitable biological sample from a patient, including, but not limited to, a blood or plasma sample, an urine sample or a cerebrospinal fluid (CSF) sample. In view of the fact that the glutamine and glycine levels described herein in accordance with the present invention are elevated above normal ranges, the elevated glutamine and elevated glycine levels are also referred to herein as xe2x80x9cabnormalxe2x80x9d or as an xe2x80x9cabnormalityxe2x80x9d.
The term xe2x80x9ca glutamine level reducing agentxe2x80x9d is meant to refer to an agent which acts to reduce in vivo glutamine levels in a subject after the agent is administered to the subject. Glutamine levels are measured in any suitable biological sample from a patient, including, but not limited to, a blood or plasma sample, an urine sample or a CSF sample. Preferred examples of glutamine level reducing agents are phenylacetate and phenylbutyrate, although any pharmaceutically acceptable agent which acts to reduce glutamine levels is contemplated in accordance with the present invention.
Phenylacetate is metabolized to phenylbutyrate in first pass liver metabolism and is a more preferred embodiment of the agent because it is more palatable in an oral form. Phenylacetate and phenylbutyrate are commercially available from Medicis Pharmaceutical Corporation, Phoenix, Ariz.
The term xe2x80x9cglycine level-reducing agentxe2x80x9d is meant to refer to an agent which, upon administration to a subject, acts to reduce in vivo glycine levels in the subject. Glycine levels are measured in any suitable biological sample from a patient, including, but not limited to, a blood or plasma sample, an urine sample or a CSF sample. Sodium benzoate is a representative glycine level reducing agent, although any pharmaceutically acceptable agent which acts to reduce glutamine levels is contemplated in accordance with the present invention. Sodium benzoate is commercially available from Medicis Pharmaceutical Corporation, Phoenix, Ariz.
As used herein, an xe2x80x9ceffectivexe2x80x9d dose refers to one that is administered in doses tailored to each individual patient manifesting symptoms of autism sufficient to cause an improvement in the patients"" expressive and receptive language skills, attention span and focus, motor planning and/or socialization with peers, with tolerable adverse effects. Representative dosage ranges for glutamine level reducing agents and glycine level reducing agents are disclosed herein. Further, after review of the disclosure of the present invention presented herein, one of ordinary skill in the art can tailor the dosages to an individual patient, taking into account the particular formulation and method of administration to be used with the compound as well as patient height, weight, severity of symptoms, and stage of the disorder to be treated.
An effective dose and a therapeutically effective dose are generally synonymous. However, compounds may be administered to patients having reduced symptoms or even administered to patients as a preventative measure. Hence, the compound may be effective in therapeutic treatment even in the absence of symptoms of the disorder.
A xe2x80x9creceptorxe2x80x9d is a macromolecular binding site which is at least partially exposed on the surface of a cell, and has specific and limited affinity for one or more molecules called xe2x80x9cligandsxe2x80x9d, which are typically neurotransmitters or hormones in their natural and native setting in vivo and may be drugs or other compounds, whether natural or synthetic in origin. When a ligand contacts an appropriate receptor, a brief binding reaction occurs which evokes a response, such as activation and depolarization of a neuron. Most receptor molecules are proteins which straddle the membrane of a cell, with an external portion for binding reactions and an internal portion which contributes to the cellular response to ligand binding. The term xe2x80x9creceptorxe2x80x9d may include various additional components, such as an ion channel associated with a receptor, perhaps merely by proximity, which is affected by the receptor.
An xe2x80x9cagonistxe2x80x9d is a molecule which activates a certain type of receptor. For example, glutamate molecules act as agonists when they excite EM receptors. By contrast, an xe2x80x9cantagonistxe2x80x9d is a molecule which prevents or reduces the effects exerted by an agonist on a receptor. Many naturally-occurring neurotransmitters are agonists, since they activate the receptors they interact with. By contrast, artificial and/or exogenous drugs may be agonists or antagonists. For example, NMDA antagonists are drugs that can suppress excitatory activity of glutamate or glycine at NMDA receptors.
Although agonist and antagonist compounds are generally thought to interact directly with receptors to achieve their effects, such effectivity may not result from direct interaction but may involve intermediate steps or compounds. Hence, the present invention is not limited to mechanisms acting directly on affected receptors involved or thought to be involved in autistic disorders. Rather, any effect of the compounds on receptors or more generally on metabolism or symptoms of the disorder is contemplated as part of the present invention. It is further noted that both Glu and Gly are non-essential amino acids. Thus, dietary restriction of Glu and/or Gly is not preferred in lowering Glu and/or Gly levels.
C. Therapeutic Methods
In accordance with the present invention a method for treating autism is provided. The method comprises administrating a pharmaceutical composition containing an effective amount of an agent that acts to reduce glutamine levels and/or an agent that acts to reduce glycine levels in a patient, particularly a human patient, for the treatment of autism or another pervasive developmental disorder (e.g. tardive dyskinesia).
In a preferred embodiment, the autistic patient has increased levels of glutamine, increased levels of glycine or increased levels of both glutamine and glycine. Glutamine and glycine level are measured in any suitable biological sample from a patient, including, but not limited to, a blood or plasma sample, an urine sample or a CSF sample.
Glutamine level reducing agents and glycine level reducing agents (e.g. phenylbutyrate, phenylacetate, sodium benzoate) are preferably administered in amounts ranging from about 10 mg/kg body weight/day to about 1000 mg/kg body weight/day, more preferably from about 50 mg/kg body weight/day to about 800 mg/kg body weight/day, and even more preferably in amounts ranging from about 250 to about 500 mg/kg body weight/day. The use of at least about 100, 200, 300, 400 and/or 500 mg/kg body weight/day of a glutamine level reducing agent or glycine level reducing agent is further contemplated.
These dosages can be administered when the glutamine level reducing agents and glycine level reducing agents are administered alone or when the glutamine level reducing agents and glycine level reducing agents are administered together. However, in a preferred embodiment, a glutamine level reducing agent and a glycine level reducing agent are administered in lower amounts when administered together as compared to dosage amounts when the glutamine level reducing agent and the glycine level reducing agent are administered alone.
The unit dose can be administered, for example, 1 to 4 times per day. Most preferably, the unit dose is administered twice a day (BID). The dose depends on the route of administration and the formulation of a composition containing the compound or compounds. Further, it will be appreciated by one of ordinary skill in the art after receiving the disclosure of the present invention that it may be necessary to make routine adjustments or variations to the dosage depending on the combination of agents employed, on the age and weight of the patient, and on the severity of the condition to be treated.
Such adjustments or variations, as well as evaluation of when and how to make such adjustments or variations, are well known to those of ordinary skill in the art of medicine. Evaluation parameters and techniques may vary with the patient and the severity of the disease. Particularly useful evaluative techniques for autism include assessment of expressive and receptive language skills, attention span and focus, motor planning and socialization with peers.
Further, the methods of the present invention are envisioned to be beneficial in combination with certain other treatments. Such other treatments are anticipated to be those enhancing the efficacy of the present invention by acting via a similar mechanism. Additionally, such treatments may act by a different mechanism than the methods of the present invention but enhance its efficacy either in the treatment of autism or other diseases or disorders in autistic patients.
For example, the methods of the present invention can further comprise administering an NMDA receptor antagonist to the autistic patient. A representative NMDA receptor antagonist is dextromethorphan, although any pharmaceutically acceptable agent which acts as an NMDA receptor antagonist is contemplated in accordance with the present invention.
The NMDA receptor antagonist can be administered in dosages ranging from about 0.1 mg/kg body weight/day to about 10 mg/kg body weight/day, preferably from about 1-1.5 mg/kg body weight/day to about 8 mg/kg body weight/day, and more preferably in amounts ranging from about 2.5 to about 5 mg/kg body weight/day. Dosages of at least about 1, 2, 3, 4 and/or 5 mg/kg body weight/day of a NMDA receptor antagonist can also be administered.
The co-administration of a glutamine level reducing agent and a glycine level reducing agent, a glutamine level reducing agent and an NMDA receptor antagonist, a glycine level reducing agent and an NMDA receptor antagonist, or a glutamine level reducing agent, a glycine level reducing agent and an NMDA receptor antagonist in accordance with the present invention is contemplated to produce additional synergistic therapeutic effects in the autistic patient. Thus, the methods of the present invention represent a significant improvement in the treatment of autism, particularly in children.
Indeed, the methods of the present invention are based on observed biochemical abnormalities, i.e. elevated glutamine and glycine levels. As such, the methods of the present invention are contemplated to be applicable to the 75 to 80% of autistic individuals having primary autism in which no underlying cause is found.
D. Pharmaceutical Compositions
Pharmaceutical compositions for use in accordance with the present invention may be formulated in conventional manner using one or more physiologically acceptable carriers or excipients. Thus, the compounds for use according to the present invention may be formulated for oral, buccal, parenteral, rectal or transdermal administration or in a form suitable for administration by inhalation or insufflation (either through the mouth or the nose). Administration may also be accomplished by any other effective means.
For oral administration, the pharmaceutical compositions may take the form of, for example, tablets or capsules prepared by conventional means with pharmaceutically acceptable excipients such as binding agents (e.g. pregelatinized maize starch, polyvinylpyrrolidone or hydroxypropyl methylcellulose); fillers (e.g. lactose, microcrystalline cellulose or calcium hydrogen phosphate); lubricants (e.g. magnesium stearate, talc or silica); disintegrants (e.g. potato starch or sodium starch glycollate); or wetting agents (e.g. sodium lauryl sulphate). The tablets may be coated by methods well known in the art.
Liquid preparations for oral administration may take the form of, for example, solutions, syrups or suspensions, or they may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may be prepared by conventional means with pharmaceutically acceptable additives such as suspending agents (e.g. sorbitol syrup, cellulose derivatives or hydrogenated edible fats); emulsifying agents (e.g. lecithin or acacia); non-aqueous vehicles (e.g. almond oil, oily esters, ethyl alcohol or fractionated vegetable oils); and preservatives (e.g. methyl or propyl-p-hydroxybenzoates or sorbic acid). The preparations may also contain buffer salts, flavoring, coloring and sweetening agents as appropriate. Preparations for oral administration may be suitably formulated to give controlled release of the active compound. For buccal administration the compositions may take the form of tablets or lozenges formulated in conventional manner.
The methods of administration according to the present invention may include parenteral administration by injection, for example by bolus injection or continuous infusion. Formulations for injection may be presented in unit dosage form, e.g., in ampules or in multi-dose containers, with or without an added preservative. The compositions used in the methods may take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. Alternatively, the active ingredient may be in powder form for constitution with a suitable vehicle, e.g. sterile pyrogen-free water, before use. The compounds may also be formulated in rectal compositions such as suppositories or retention enemas, e.g. containing conventional suppository bases such as cocoa butter or other glycerides. In addition to the formulations described previously, the compounds may also be formulated as a preparation for implantation or injection. Thus, for example, the compounds may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt.